Biased ferromagnetic multiport microwave circulator



June 9, 1964 c. BOWNESS 3,136,952

BIASED FERROMAGNETIC MULTIPORT MICROWAVE CIRCULATOR Original Filed April 4, 1960 FIG. 3 44 1 45 40 INVENTOR aou/v BOW/V555 A TTO/P/VEY 3,136,962 BIASED FERROMAGNETIC MULTHPORT MICROWAVE CIRCULATOR Colin Bowness, Weston, Masa, assignor to Raytheon Company, Lexington, Mass, a corporation of Delaware Continuation of application Ser. No..19,642, Apr. 4, 1960. This application Sept. 25, 1963, Ser. No. 312,252

11 Claims. (Cl. 333-]..1)

1 This is a continuation of copending United States patent application No. 19,642, filed April 4, 1960, now abandoned.

This invention relates in general to microwave circulators and more particularly to symmetrical microwave circulatorsutilizing ferrite materials as the effective agent.

The term microwave circulator is descriptive of nonreciprocal or one way multiport coupling networks which generally employ ferromagnetic or ferrite material for shifting the plane of polarization or the phase of the propagated wave, and generally hybrid junctions or twornode transducers for coupling the network to a waveguide system, An informative dissertation on the basic operation of microwave circulators is to be found in the article by C, L. Hogan, Reviews of Modern Physics, vol. 25, No. 1. As is now well known, the electromagnetic Wave transmission art has been substantially advanced by the development of a whole new group of nonreciprocal transmission components. A large number of these have utilized one of the nonreciprocal properties of gyromagnetic. material most often designated ferromagnetic materials or ferrites. One of the more important of these components is the multibranch network known as a "r'n'icrowave circulator circuit. While the several circulators heretofore invented have had different physical apparatus and structural arrangements, each having its own specific advantage and usefulness, each has had the electrical property that energy is transmitted in circular fashion around the branches of the network so that energy appearing in one branchthereof is coupled to only one other branch for a given direction of transmission but to another branch-for the opposite direction of transmission. This afforded a circuit component with an entirely new electrical property. V

Numerous applications of the circulator as a circuit element have been devised. It has been included in modulator circuits and in compressing and expanding circuits. It has been used as a TR-box type coupling between an antenna, transmitter, and receiver circuits, as a channel dropping or branching circuit in multichannel microwave systems, and in many other applications. Numerous other applications are being continuously conceived.

While a variety of microwave circulators are available, the majority of these multiport devices are extremely complex. Whereas, substantially all of the heretofore known circulators having required hybrid junctions or two-mode transducers it will be appreciated that they have been quite? cumbersome, as well as expensive to construct.

xTwo basic methods of making a circulator are well known. Firstly, a circulator can be made by employing thediiferential phase shift characteristic of a ferrite loaded waveguide, and secondly, by employing the Faraday rotation characteristic, i.e., the rotation of the plane of polarization of the electric fields in an electromagnetic wave'. The first type requires two wave-guide hybrid junctions to complete the circulator and the second type requires two two-niodetransduce'rs or a six-port turnstile junction. i 'Although a reciprocal lossless three-port junction cannot 'be matched in all arms, a third type of simple and inexpensive microwave circulator which can be matched, while limited to three ports, may be found in a 120 degree Y-junction with aferrite disc orrod placed at the geo- Patented June 9, 1964 metrical axis and a magnetic field applied along the axis. The utility of the last-mentioned circulator is severely limited because of the previous inability to extend or expand it in its simplified form to N ports where N is greater than three. For example, in order to provide a four-port circulator of the aforementioned third type referred to immediately hereinabove, it was believed that this could only be done by combining two three-port Y-junctions.

Heretofore, so far as is known, in order to expand the aforementioned third type of circulator to a four-port circulator it was believed that such a four-port circulator could be provided only by combining two complete threeport circulators. In other words, to provide an N port circulator of the aforementioned third type where N is greater than three, N 2 three-port Y-junctions were required.

It may now be readily apparent that a simplified and relatively inexpensive N port microwave circulator, where N is greater than three is needed and would be welcomed as a highly desirable advancement in the art.

It is, therefore, a principal object of the present invention to provide a simplified and inexpensive N port micro wave circulator where N is greater than three.

It is another object of the present invention to provide a compact single junction microwave circulator which is relatively economical to construct.

It is still another object of the present invention to provide a single junction nonreciprocal coupling means having a convenient terminal arrangement adaptable to a variety of circulator applications.

Briefly, the present invention comprises a nonreciprocal N port microwave circulator, where N is greater than three, that may be-matched in all. arms wherein all of the ports are symmetrical one with another and extend outwardly from a geometrical or common central axis. Perrite-material axially symmetrical about the geometrical axis is located at'oradjacent the geometric axis and within the circulator and a magnetic field is provided along the geometrical axis. V 7

These and other objects and features of the invention,

Y together with their incident advantages, will be more tion; and

FIGQ3 is a fragmentary sectional view of the center portion of a circulator in accordance with the present invention. s

An exemplary embodiment of the invention shown by way of example in FIG. 1 as a six-port circulator 10, comprises six arms 11 through 16 of rectangular waveguide symmetrically located one with another and extending outwardly from the geometrical axis 17 of the circulatori For a symmetrical circulator having six ports it is obvious that the longitudinal axes of the arms are equidisposed with respect to each other, are located 60 degrees apart, and that each said longitudinal" axis lwill intersect the geometrical axis 17. It is. essential that a circulator constructed in accordance with the present invention be symmetrical abouta geometrical axis. The number of ports that may be used is theoretically not limited butpractical Obviously, if the over-all size of the circulator is in-.

creased, i.e., the open central'portion 13 thereof is made larger, more ports for a particular wavelength of operation may be provided. Within the central part 18 of the circulator a means is provided for effecting coupling of wave energy from any one port to, for example, another port, such as, forexample, the next adjacent port. The aforementioned meansas shown in FIG. 1 comprises a hexagonal rod or disc 19 of ferromagnetic or ferrite material located on and about the geometrical axis 17 of the circulator 10. A magnetic field represented by the arrow 20 is provided as indicated along the geometrical axis 17 and longitudinally through the ferrite 19. Any suitable and well-known means (not shown) such as, for example, a permanent magnet, electromagnet or the like may be used to provide the magnetic field. The means for providing the magnetic fields in FIGS. 1 and 2 have not been shown for reasons of simplicity since such arrangements are well known in the art and would only unduly complicate the drawings. The direction of the magnetic field determines the direction of circulation,

hence the direction of circulation may be reversed by simply reversing the direction of the magnetic field. In the case of an electromagnet, this may be simply accomplished by reversing the current through the coil of the electromagnet. High speed switching may be provided by reversal of the magnetic field in any convenient and conventional manner and high speed modulation may be likewise provided by variation of this field.

Although a hexagonal rod or disc 19 has been shown in FIG. 1, it is to be understood that other suitable configurations may be used so long as axial symmetryris maintained. For example, a circular rod may be used, the apexes of a rod formed with a hexagonal shape for a six-port circulator (square for four-port, octagonal for eight-port, etc.) may be located on the longitudinal axes of the ports 11 through 16, the fiat sides of a hexagonal structure or the like may be located perpendicular to the axes of the ports 11 through 16, or ferrite material may be provided on opposite walls on the inside of each port at the point where the wall of each port forms an apex with the wall of the next adjacent port. It is essential only that axial symmetry of the effective ferrite material, whether a single unit or a plurality of components, be maintained.

FIG. 2 shows a five-port E-plane circulator 30 constructed in essentially the same manner asthe circulator shown in FIG. 1 with the exception that the arms 31 through 35 are now 72 degrees apart and the ferrite material, shown as a circulator rod 36, is located along the geometrical 'axis 37 of the circulator and between the top and bottom wall thereof. For an E-plane circulator the effective ferrite material is parallel to the longitudinal axis of the ports whereas for an H-plane circulator the ferrite material is parallel to the short sides of the ports.

In operation, if wave energy is coupled by any suitable means to any one arm of the circulator, substantially all of the wave energy will be coupled to another arm by reason of the action of the ferrite material constructed, arranged and adapted to operate as and for the purposes described hereinabove.

For optimum operation it may be desired or considered necessary to provide matching means within the circulator. Such matching means may be comprised of one or more posts, irises, buttons, transformers,,or the like well known in the art. One requirement is essential however. As with the ferrite, the matching means must be symmetrical about the geometrical or common central axis. If a post, for example, is provided in each port they must all be substantially symmetrically located with respect to the central axis and, if a single post is used, its longitudinal 44. Afiixed, to button 41 is a cylindrical post 45 of dielectric material which extends toward button 40. The longitudinal axisof matching post 45 is also coincident with the central axis 44. In certain applications, the post 45 may be in contact with both buttons 40, 41 since the degree of mismatch will determine the diameter and length of the post. The dielectric material for the post may be Teflon, polystyrene or the like.

By way of example, for an operating frequency of about 9,000 megacycles and a circulator formed of rectangular waveguide 0.9 inch by 0.4 inch, a ferrite rod having a diameter of about one-third the width of the, circular ports and a length equal to the inside height of the circulator may be used.

In practice the applied magnetic field, the size and shape of the ferrite and the position of suitable matching posts or structures may be varied to achieve the required conditions of matching and operation as a circulator. Structures have been built in Z-band waveguides which demonstrated the aforementioned and desired properties of this invention.

While I have shown and described particular forms of embodiment of my invention and described particular methods for use of my invention, I am aware that various minor changes therein will readily suggest themselves to those skilled in the art without departing from the spirit and scope of my invention.

It is, therefore, to be understood that within the scope of the appended claims my invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a microwave circulator for use in a waveguide system the combination comprising: a symmetrical junction having at least four rectangular waveguide ports capable of supporting a single dominant mode of propagated Wave equidisposed with respect to each other about a common central axis; at least one circular ferromagnetic rod attached to one wall of said junction and axially symmetrical with respect to said common axis, the surface of said rod being'planar in a direction parallel to the largest transverse electrical dimensions of said ports; an

elongate post of dielectric material axially symmetrical with respect to said common axis; and means for applying a magnetic field to said rod in the direction of said common axis.

2. In a microwave circulator for use in a waveguide system, the combination comprising: a symmetrical junction having five rectangular waveguide ports capable of supporting a single dominant mode of a propagated wave equidistant with respect to each other about a common central axis; a ferromagnetic rod disposed within said junction and along said common axis, the surface of said rod being planar in a direction parallel to the largest transverse electrical dimensions of said ports; and means for applying a magnetic field along said axis.

3. In a microwave circulator for use in a waveguide 7 system, the combination comprising: a symmetrical juncaxis must be substantially coincident with the aforemenaxes of buttons 40, 41 are coincident with the central axis tionhaving six rectangular waveguide ports capable of supporting a single dominant mode of a propagated wave equidistant with respect to each other about a common central axis; a ferromagnetic rod disposed within said junction and along said common axis, the surface of said rod being planar in a direction parallel to the largest transverse electrical dimensions of said ports; and means for applying a magnetic field along said axis.

4. A microwave circulator comprising a symmetrical junction having at leastfour waveguide ports capable of supporting a single dominant mode of a propagated wave, said ports disposed in a common plane and extending radially from a common central axis and'being'spaced equidistant from one another throughout their lengths and being coupled together only in the area. of said common axis, said ports intersecting adjacent said axis, said intersection defining a nonresonant area in the vicinity of said. axis, and means for directing microwave energy from a respective waveguide through said coupled area and outwardly through only one adjacent waveguide.

5. A microwave circulator substantially as set forth in claim 10 wherein said means comprises a ferromagnetic element located on said axis, and means for applying a magnetic field along said axis.

6. A microwave circulator substantially as set forth in claim 5 wherein said ferromagnetic element is a cylindrical rodlike member.

7. A microwave circulatorsubstantially as set forth in claim 5 wherein said ferromagnetic element is rodlike in shape and has on its circumference a number of planar surfaces corresponding to the number of ports, each planar surface facing and being disposed substantially perpendicular to the longitudinal axis of a respective port.

8. A microwave circulator substantially as set forth in claim 5 wherein said ferromagnetic element includes an elongate post of dielectric material axially symmetrical with said axis.

9. A microwave circulator substantially as set forth in claim 5 wherein said ports are identical 10. A microwave circulator comprising a symmetrical junction embodying a nonresonant central area having a References Cited in the file of this patent UNITED STATES PATENTS 2,951,216 Nelson et al Aug. 30, 1960 OTHER REFERENCES Chait et al.: NRL Progress Report, March 1958, page 50.

Electrical Manufacturing, February 1959, pages 61-63.

Swanson et al.: 1958 IRE Wescon Convention Record, Part I, pages 151-156. 

1. IN A MICROWAVE CIRCULATOR FOR USE IN A WAVEGUIDE SYSTEM THE COMBINATION COMPRISING: A SYMMETRICAL JUNCTION HAVING AT LEAST FOUR RECTANGULAR WAVEGUIDE PORTS CAPABLE OF SUPPORTING A SINGLE DOMINANT MODE OF PROPAGATED WAVE EQUIDISPOSED WITH RESPECT TO EACH OTHER ABOUT A COMMON CENTRAL AXIS; AT LEAST ONE CIRCULAR FERROMAGNETIC ROD ATTACHED TO ONE WALL OF SAID JUNCTION AND AXIALLY SYMMETRICAL WITH RESPECT TO SAID COMMON AXIS, THE SURFACE OF SAID ROD BEING PLANAR IN A DIRECTION PARALLEL TO THE LARGEST TRANSVERSE ELECTRICAL DIMENSIONS OF SAID PORTS; AN ELONGATE POST OF DIELECTRIC MATERIAL AXIALLY SYMMETRICAL WITH RESPECT TO SAID COMMON AXIS; AND MEANS FOR APPLYING A MAGNETIC FIELD TO SAID ROD IN THE DIRECTION OF SAID COMMON AXIS. 